Shock and vibration induced damage or performance degradation of electronic components is an ongoing problem associated with electronic assemblies. These problems become even more acute for complex electronic devices, such as cellular telephones, that contain sensitive electronic components, such as certain LCD displays and microelectronic devices or packages, and which are adapted to be hand-held and/or carried on the body of a user and, as such, are subject to a relatively harsh vibration and shock environment.
By way of example, Chip Scale Packages (CSP's) are one type of microelectronic device that are increasingly utilized in cellular telephones and that are relatively sensitive to shock and vibration. This is due, in part, to the flexible, thin layered construction of CSP's and to the manner in which CSP's are attached to a distribution circuit, such as on a printed circuit board. More specifically, CSP's are attached to distribution circuits by solder balls which form the electrical and mechanical interconnect structure. The mechanical integrity of such solder ball attachments is generally lower than for conventional leaded parts, such as Quad Flat Packs or Thin Small Outline Packages. Additionally, solder ball attachments leave relatively large spans of the CSP unsupported.
One approach to solving vibration and shock induced performance degradation and damage in CSP's is to use a polymer underfill to bond the CSP to a printed circuit board. However, this solution is less than optimum because it generally requires added processing steps and increases the difficulty of repair after the CSP is bonded to the printed circuit board, both of which increase manufacturing costs. More specifically, the use of a polymer underfill typically requires special application techniques using a special polymer compound which possesses low viscosity in an uncured state, yet cures to form a high modulus structure. The processing times required to allow the underfill to wick into the gap between a CSP and a printed circuit board, and to subsequently cure the underfill, usually involves a batch processing technique which is generally incompatible with a continuous manufacturing line. Further, after bonding, the difficulties with reworking the underfilled CSP discourages some manufacturers from implementing any rework process.